1. Field of the Invention
The present invention relates to a slit lamp and an attachment dismountably attached to a slit lamp to make possible observation and recording of a section of the crystalline lens of a patient's eye.
2. Descriptions of Prior Art
A slit lamp is a device for projecting a slit pattern light to the crystalline lens of a patient's eye and observing and recording the projected portion. In one mode of observation, an optical sectional image is observed by viewing the crystalline lens of the patient's eye in a direction oblique to the slit projection plane. When this method is carried out with an ordinary optical system, it is impossible to obtain a satisfactorily focused image throughout the entire optical section of the crystalline lens. It has been known that the entire optical sectional image of the crystalline lens can be observed in the well-focussed state with an optical system having an image plane containing the intersecting line between the slit plane including the slit pattern light projected to the eye ball and the principal plane of the imaging optical system in the observation optical system. An apparatus for observing the section of the crystalline lens by utilizing this principle is disclosed, for example, in Japanese patent application No. 52-18511. This known apparatus is used exclusively for observation of the section of the crystalline lens, and the apparatus cannot be used as a slit lamp for other observation methods. This known apparatus is advantageous in that the entire optical sectional image of the crystalline lens formed by the slit projection light can be observed in the well-focused state. However, since one observation is limited to one section, a long time is required for observing the patient's eye entirely and discomfortable feeling is given to the patient. Furthermore, the apparatus is not provided with means for recording the position where the slit light projection is made in patient's eye. Accordingly, in case of examination of, for example, cataract, the apparatus is not suitable for precisely judging the position of the nebula and observing and recording the progress of disease.
As means for observing the entire image of the crystalline lens, there is known a retroillumination method in which a slit light is projected to patient's eye and the crystalline lens is illuminated with the slit projection light reflected from the eye fundus. It also is known that in order to prevent inclusion of a harmful cornea-reflected light into the observation optical system when observation is carried out according to this retroillumination method, a polarizer is arranged in the illumination system and an analyzer is arranged in the observation system. For example, this arrangement is disclosed in Japanese Publications "Clinical Ophthalmology", Volume 32, No. 6 (June 1978) and "Acta Societatis Ophthalmologicae Japoncae", Volume 62, 1958, Page 380. However, in the conventional apparatus utilizing the retroillumination method, uniformity of the direction of the illumination by the slit pattern light, uniformity of the quantity of the illumination light, direction and uniformity of the observation direction are not guaranteed, and the apparatus is not suitable for recording and measurement.